1. Field of the Invention
The present invention relates to a curable epoxy resin composition useful for surface treatment to impart water-repellency or ink-repellency to an article surface, especially to an epoxy resin composition for forming a coated film (coating) in a pattern by UV irradiation. The present invention also relates to a surface treatment method employing the epoxy resin composition; a liquid ejection recording head having been treated for ink repellency with the resin composition, and a liquid ejection recording apparatus employing the liquid ejection recording head.
2. Related Background Art
Generally, in many application fields, methods are known for providing a member with water-resistant or ink-repellent properties by applying a water-repellent paint, and resin materials and paints for the methods have been developed. For example, the coating formed from a fluorine-type paint having a fluoropolyolefin group or a perfluoro group is sufficiently stable thermally and chemically, and it has excellent weather resistance, water resistance, chemical resistance, solvent resistance, and the like properties. Such coating has high mold releasability, abrasion resistance, and water repellency, and is used in various application fields.
On the other hand, liquid ejection recording heads, which eject liquid droplets through an ejection orifice onto a paper sheet or a like recording medium to conduct recording or to form an image, are being improved for higher recording performance with a smaller liquid droplet size, a higher driving frequency, and a larger number of nozzles. Therefore, the treatment to keep the surface condition of the nozzles unchanged is becoming more important.
However, it is difficult to conduct a surface treatment selectively or in a precise pattern to prevent ink from adhering to the nozzle surface due to the following reasons. For the above-mentioned fluorine-type paint to function like a photoresist, the paint should be mainly composed of a substance having a photosensitive functional group. However, such a molecule cannot readily be designed to also be water-repellent or ink-repellent.
Furthermore, even if the surface treatment can be made satisfactory by the use of a conventional fluorine-type material, the coating structure should be designed to maintain the surface properties for a long period of time. The surface treatment material yielding the above properties in a pattern is highly useful in treatment of the surface of a liquid ejection recording head (ink-jet printing head), as is explained below.
For the ink-jet recording system to conduct a recording by ejection of ink droplets, the ejection orifice (opening) is preferably designed to have the following performance:    1. The ink column of remaining unejected droplets can be quickly put back into the nozzle.    2. The ink droplets adhering to the surface can readily be swept out by a cleaning operation.    3. The ink droplets adhering to the surface should be resistant to scratching in a cleaning operation and paper sheet delivery.    4. In repeated liquid droplet formation and ink-refilling, a meniscus should be formed at the position of the nozzle face (“23” in FIG. 1).    5. The normal line of the meniscus should be directed to the droplet ejection direction.    6. The interfacial tension or the contact angle should be sufficient even for an ink having a low surface tension, or even under low negative pressure conditions.
In the liquid ejection recording head, the ejection orifice should have the above properties, because the recording liquid, such as ink, adhering to the periphery of the orifice will cause a deviation in the direction of the ejection (flight) of the liquid droplets to render the printing imprecise and will directly impair the printing performance. Methods of water-repellency treatment of the ejection orifice face are known to prevent the adhesion of liquid at or around the ejection orifice, so as not to cause a deviation of the ejection direction.
An example of the related prior art techniques is an ink-repellency treatment with a polymer having a fluoroacetyl group and a silazane group (e.g., Japanese Patent Application Laid-Open No. 2-39944, etc.). On the other hand, with greater needs for image recording by a printer of the liquid ejection recording system, the properties of the recording liquid are required to be further improved. Since, such a recording liquid is usually formulated to be basic (pH 7-11) for higher dissolution stability or higher dispersion stability of the contents, the members of the printer are preferably made from a construction material having high alkali resistance and high hydrolysis resistance.